Optical-fiber cables are often needed to withstand harsh environments. For example, cables deployed within geothermal wells need to be able to withstand high temperatures.
Some conventional cable components are unsuitable for use at high temperatures. For example, thixotropic gels, which are commonly used to provide water-blocking and coupling functionality, are typically unable to withstand such high temperatures. Accordingly, optical-fiber cables intended for high-temperature operations typically employ dry designs, which eliminate the thixotropic gel from the optical-fiber cable.
One problem associated with dry-cable designs is that the optical fibers contained within the cable are often insufficiently coupled to the cable and/or buffer tube enclosing the optical fibers. In the absence of sufficient coupling, the optical fibers can bunch up or stretch inside the cable, which can lead to undesirable attenuation.
In addition to possessing high temperatures, geothermal wells also typically possess a hydrogen-rich environment. Hydrogen may diffuse into optical fibers and react with the silicate glass, thereby producing hydroxide ions. This reaction damages the optical fiber, quickly rendering it useless in hydrogen-rich environments.
There is currently no optical-fiber cable that is capable of withstanding the high-temperature and hydrogen-rich environment of geothermal wells for an extended period (e.g., more than a few days).
Accordingly, a need exists for an improved loose-tube optical-fiber cable that is capable of functioning in high-temperature and hydrogen-rich environments.